Sir Keir Starmer and Donald Trump have discussed the urgent need to reopen the Strait of Hormuz amid ongoing tensions in the Middle East.
The key shipping route, which handles around a fifth of global oil and gas supplies, has seen traffic fall about 95% since the Iran bar began on February 28.
A Downing Street spokesperson said both leaders "agreed that reopening the Strait of Hormuz was essential to ensure stability in the global energy market".
The call comes ahead of a Cobra meeting chaired by the prime minister on Monday, which will be attended by Bank of England governor Andrew Bailey to discuss the impact of the war on the cost of living.
Iran has effectively shut down the strait following US and Israeli strikes, triggering a surge in global fuel prices, with crude up 45% to $106 a barrel.
Over the weekend, the US president threatened to "obliterate" Iranian power plants if the Strait was not opened within 48 hours.
Tehran has said it would target US-linked energy sites across the Gulf region if the US follows through with its threat, according to Iranian state media.